Diagnose by symptom
White coating on leaves
A white, powdery or cottony coating is usually mildew or a pest colony. Check what exactly you see:
Diseases
Powdery mildew
A white, powdery coating on leaves, shoots and buds. The leaves turn yellow, become deformed and drop prematurely. The c…
DiseaseDowny mildew
Yellow or angular (vein-bounded) spots on the upper leaf surface, matched underneath by a grey-violet or brown coating o…
Pests
Frequently asked questions
What is the white powdery coating on my leaves?
It is usually powdery mildew – a fungal disease that leaves a white, floury coating on the upper leaf surface, shoots and buds. It develops in warm, dry weather with high air humidity, especially where plants stand too densely. The coating can initially be rubbed off with a finger.
What is the difference between powdery and downy mildew?
Powdery mildew forms a white coating on the upper leaf surface and favors warmth and dryness. Downy mildew shows yellow spots on top and a grey-violet growth on the leaf underside, developing in cool, damp conditions. They are different fungal groups, so control differs too.
How do I get rid of powdery mildew?
Remove and discard infected leaves, thin the planting, and improve air flow while avoiding wetting the foliage when watering. Sprays based on sulphur, potassium bicarbonate, or ready-made mildew fungicides can help. Avoid over-fertilising with nitrogen, since soft growth is more susceptible.